Pinch valves are well known for controlling the flow of fluid. Generally, a pinch valve includes a flexible conduit which in a normal or relaxed state provides a fluid flow path. A pinch mechanism operates to pinch or collapse the conduit and thus interrupt the fluid flow therethrough. Pinch mechanisms may be simple manually operated screw-type devices or more complex motor or solenoid operated devices controlled by electric signals.
Multi conduit pinch valves are known in the art for controlling fluid flow through a plurality of conduits in a synchronized fashion. For example, U.S. Pat. No. 4,457,339 to Juan et al. discloses a multi-programmable pinch valve module including a cam disk with four cams formed thereon. A plurality of hollow cylindrical rollers may be movably disposed about the periphery of the cam disk. As the cam disk rotates, the individual radial lobes about the periphery of the cam disk press the hollow cylindrical rollers into engagement with flexible conduits. The sequence in which the various flexible conduits are pinched closed may be adjusted or programmed by moving the hollow cylindrical rollers to various positions around the periphery of the disk.
Another form of multi conduit pinch valve is used in an instrument known as the E4A.TM. Electrolyte Analyzer manufactured and sold by Beckman Instruments, Inc., Brea, Calif. The pinch valve used therein includes a D-shaped shaft over which a plurality of individual cams may be placed. Various cams have different lobe combinations and orientations with respect to D-shaped holes in the center of cams. As the shaft and thus the cams rotate, the cams operate spring loaded pinch elements which pinch or release flexible conduits fixed between the pinch elements and a backing bar or plate. By selecting particular cams, the valve can be programmed to provide predetermined combinations of pinched and released flexible conduits. The valve assembly may be reprogrammed by removing the shaft and replacing the cams with cams of differing lobe combinations and/or orientations.
Each of the above valves, however, has drawbacks and limitations which are particularly troublesome in automated applications. For example, only a relatively limited number of flexible conduits can be controlled by the valves. The valve disclosed by Juan et al. shows applicability to four flexible conduits while the pinch valve in the E4A Analyzer controls up to six conduits. Also, the reprogramming of the valves can be difficult and time consuming, requiring substantial manual effort. More importantly, both of the valves limit the number of combinations of open and closed conduits available. For example, if a multi conduit valve accommodates six conduits, a total of sixty-four on-off combinations are possible. However, if the valve has only four states in each cycle, then only four of the possible sixty-four combinations may be utilized.
Another serious drawback is that the various valve on-off combinations are associated with respective disk or shaft angular positions. In order to change from one on-off combination to another such combination, it may be necessary for the disk or shaft to rotate through angular positions corresponding to unwanted combinations. Accordingly, conduits that are to remain open may be briefly closed while the disk or shaft rotates through unwanted combinations and conduits that are to remain closed may likewise be briefly opened, resulting in unwanted fluid interruption or flow that may have serious effects on the performance of the automated system.
Thus, there is a need for a pinch valve that can accommodate a large number of fluid conduits yet that allows easy programming of the on-off conditions for each of the conduits. Furthermore, there is a need for a pinch valve that does not limit the combinations of pinched and unpinched conduits to some number smaller than the number of possible combinations and does not pinch or release unwanted conduits while changing from one combination to another.